A plasma display panel (PDP) is a flat display device using a plasma phenomenon to display an image in the plasma display panel. The plasma phenomenon is also called a gas-discharge phenomenon since a discharge is generated in the panel when a potential greater than a certain level is applied to two electrodes separated from each other under a gas atmosphere in a non-vacuum state.
Currently used plasma display panels generally use an alternating current (AC) driven plasma display panel similar to that shown in FIG. 1. The AC plasma display device has a fundamental structure in which a front substrate 1 is disposed facing a rear substrate 3, with a discharge space 5 between the two substrates. On the front substrate 1, a plurality of pairs of sustain electrodes are formed in a pattern, each comprising a scan electrode X, and a common electrode Y. Each of the scan electrode X and common electrode Y comprises a transparent electrode 7 and a metal film 9. A dielectric layer 11 is also coated over the front substrate and sustain electrodes for the AC driving. The surface of the dielectric layer 11 is coated with an MgO passivation layer 13. On the rear substrate 3, a plurality of address electrodes A are provided and are covered by a dielectric layer 15, and a plurality of barrier ribs 17 with corresponding red, green and blue phosphor layers 19R, 19G, and 19B formed between adjacent barrier ribs.
The front substrate is disposed facing the rear substrate and the two are sealed to one another. The internal space thereof is evacuated to reach a near vacuum state, and the discharge gas is injected therein. The discharge gas may include any one or a mixture of inert gasses such as He, Ne, or Xe. Such a PDP includes an array of groups of three electrodes with corresponding red, green and blue phosphor layers, 19R, 19G and 19B. When a predetermined voltage is applied across the two electrodes to induce plasma discharge, the fluorescent layer is excited by UV rays generated by the plasma discharge, and visible light is emitted.
Typically, the phosphor used for the PDP is a phosphor that is excited by ultraviolet rays. Because green has the highest fraction of white brightness among red, green and blue, the green brightness is the most important for improving the PDP brightness. Currently, Zn2SiO4:Mn, BaAl12O19:Mn, or (Ba,Sr,Mg)O.αAl2O3:Mn (where α is an integer from 1 to 23) are used for the green phosphor, and of these, Zn2SiO4:Mn is the most popular due to its better brightness characteristics. However, it also has shortcomings in that the discharge characteristics tend to degenerate as is discussed in further detail below.
As shown in FIG. 1, since the MgO layer 13 of the front substrate 1 and the phosphor layers 19R, 19G, 19B of the rear substrate 3 are directly exposed to the discharge space, the secondary electron emission coefficient of the MgO layer and the surface charge of the phosphor layer are directly affected by the amount of wall charge piled up on the phosphor layer and the MgO layer. During positive surface electrification, discharge failure is rarely generated, while during the negative surface electrification, discharge failure is common. This tendency is largely dependant on the driving system. In order to increase discharge stability and to decrease discharge failure, the red, green, and blue phosphors are generally selected so that the surface electrification characteristic is positive regardless of color. Nevertheless, Zn2SiO4:Mn, the most popular green phosphor, has a negative surface electrification characteristic. Accordingly, when the PDP is driven in a driving waveform sensitive to the surface electrification characteristics of the phosphor layer, that is, the variation of the rear substrate, the discharge voltage of the green cell is higher than those of the red cell and the blue cell.
The mechanism to increase the discharge voltage may be described as follows: upon the reset discharge, the characteristic of driving an alternating current plasma display during the real discharge, that is, before the discharge voltage is applied to the address electrode terminal, the wall charge is piled up. Before the discharge voltage is applied to the address electrode terminal, wall charges having opposite polarities are respectively piled up on the front substrate and the rear substrate. Thereby, a voltage differential is generated between the front and rear substrates.
When the voltage differentiation reaches a certain level, a voltage having the same polarity as the wall charge piled up on both the address electrode terminal and the scan electrode terminal is applied to discharge. Thereby, the address discharge voltage is lowered by effectively piling the wall charge at an appropriate level. Before the discharge voltage is applied to the address electrode terminal, the cations pile up on the surface of the phosphor layer of the rear substrate as a wall charge. As the Zn2SiO4:Mn having negative surface electrification characteristics is counterbalanced by the wall charge of cations, the green cell generates a smaller discharge voltage that those of the red cell and blue cell. Accordingly, the green cell of Zn2SiO4:Mn may require a higher address voltage compared to the red cell or the blue cell, and sometimes, discharge failure occurs.
In order to solve the problems relating to Zn2SiO4:Mn, Korean Patent Laid-Open Publication No. 2001-62387 discloses a green phosphor in which YBO3:Tb is added to Zn2SiO4:Mn. However, the obtained green phosphor has deteriorated color purity. Further, Korean Patent Laid-Open Publication No. 2000-60401 discloses a green phosphor in which a positive charged material of zinc oxide and magnesium oxide is added to Zn2SiO4:Mn. However, the green phosphor obtained from this method also causes problems in that the color purity and the lifespan are deteriorated. Further, Japanese Patent Laid-Open Publication No. 2003-7215 discloses that a mixture of manganese-activated aluminate green phosphor and terbium-activated phosphate or terbium-activated borate green phosphor can improve the driving voltage and the brightness failure. However, the afterglow properties of green phosphor cannot be improved sufficiently and there are limits for improvement of UV collusion resistance and lifespan characteristics by the above methods.